1. Field of the Invention
The present invention relates to connectors for use in a microphone, and in particular relates to a shielding structure and shield method against high frequency current attempting to enter from the outside.
2. Related Background of the Invention
In a microphone in which miniaturization is required, such as a certain type of microphone, e.g., a tiepin type microphone, a gooseneck type microphone, and the like, in order to make the microphone unnoticeable a low cut circuit and an output circuit are housed in a circuit housing part provided separately from a microphone unit part, and the above-described microphone unit part and circuit housing part are connected by a dedicated microphone cable. In the microphone unit part, sound is converted into an electric signal, and this sound signal is transmitted to the above-described circuit housing part to be output from the output circuit incorporated in the circuit housing part. The circuit housing part incorporating the low cut circuit and output circuit is called a power module part. In case of a condenser microphone, an impedance converter is incorporated in a microphone unit part.
The dedicated microphone cable for connecting the microphone unit part and the power module part is a two-core shielded cable. This microphone cable includes signal wires for inputting to the power module part the sound signal output from the microphone unit part, and a shield outer jacket for electrostatically shielding and grounding these wires. In case of a condenser microphone, the above-described signal wires of the microphone cable also serve as power supply wires for supplying power to the impedance converter from the outside.
Because the sound signal converted at the microphone unit part is transmitted to the power module part through the above-described dedicated microphone cable under unbalanced condition, it has a drawback of being vulnerable to noise from the outside, i.e., being susceptible to electromagnetic waves from the outside. More specifically, when electromagnetic waves reach the dedicated microphone cable from the outside, the electromagnetic waves enter the inside of the microphone unit part or the power module part through this microphone cable, and the electromagnetic waves are detected by semiconductor elements constituting the microphone unit part or the power module part, and this results in noise that will mix with the sound signal. Moreover, from the power module part the microphone output is output through a balanced shielded cable, however, if a strong electromagnetic wave reaches the microphone or an output cable of the microphone, it turns into a high frequency current and enters the inside of the microphone via the microphone connector. This current is detected by the above-described semiconductor elements, resulting in noise that will mix with the sound signal. In case of a condenser microphone, a high frequency current that is transmitted to the microphone unit part via the microphone connector is detected by the semiconductor elements constituting the impedance converter, resulting in noise, and therefore, the condenser microphone is more susceptible to electromagnetic waves.
From the microphone, more specifically from its power module part, sound signals are output through the microphone cable comprised of a balanced shielded cable as described above. The microphone cable is configured so as to be removably mounted to the microphone by a 3-pin microphone connector defined by EIAJ RC-5236 “a latch-lock round connector for audio equipment”. In the 3-pin microphone connector, typically, a first pin is used for grounding, a second pin used as the hot side of a signal, and a third pin used as the cold side of a signal.
A connector attached to an ordinary microphone cable has a male connector and a female connector engaging each other for contact, wherein in at least one of the male connector and the female connector, two core wires of the microphone cable are directly connected to the second pin and third pin by soldering or the like, respectively. A shield outer jacket of the microphone cable is connected via a lead wire to the housing of the above-described connector made of metal. For this reason, there is impedance for high frequency between the shield outer jacket of the microphone cable and the connector housing, and from this part a high frequency current enters.
Conventionally, with regard to microphone-related shielding techniques, although surrounding the microphone body with a cylindrical shielding member has been proposed (for example, see Patent Document 1 and Patent Document 2), shielding the connector portion, as has been described above, has not been of major interest. For this reason, high frequency electromagnetic waves enter from the connector portion, causing noise that will mix with the sound signal.
In particular, because high frequency electromagnetic waves exist nearby everywhere due to the popularization of mobile phones and the like as in recent years, there are more chances that a high frequency signal enters from the connector portion of the microphone cable and noise enters into the sound signal. In particular, in case of a condenser microphone, the use of a mobile phone or the like near the condenser microphone presents a problem that the condenser microphone is susceptible to a high frequency signal emitted from the mobile phone and the high frequency signal entering from the connector portion is likely to become noise.
Therefore, the present inventor filed a patent regarding a microphone connector and a method of shielding the same, earlier. Here, the microphone connector includes a crimping sleeve made of shield material and having a small-diameter cylindrical part and a large-diameter cylindrical part, wherein the small-diameter cylindrical part of the crimping sleeve fits around the outer peripheral side of a fold-back part of a shield outer jacket at an end portion of a microphone cable and is compressed, and thereby the crimping sleeve is coupled with the microphone cable, and wherein the large-diameter cylindrical part of the crimping sleeve covers a connection portion between the connector and the microphone cable, so that the large-diameter cylindrical part of the crimping sleeve and the connector housing engage each other (see Patent Document 3).
[Patent Document 1] Japanese Patent Application Laid-open No. 2002-152892
[Patent Document 2] Japanese Patent Application Laid-open No. 11-155198
[Patent Document 3] Japanese Patent Application Laid-open No. 2006-61765
FIGS. 8A, 8B, 8C and 9 show an example of a microphone connector described in Patent Document 3. In FIGS. 8A, 8B, 8C and 9, reference numeral 10 represents a female connector. To the female connector 10, a male connector at a microphone (not illustrated) side is inserted to connect the female connector 10 and the male connector electrically. The female connector 10 is a so-called 3-pin type, and includes: three pins to be engaged with the male connector at the microphone side; and terminals electrically integrated with these pins and projecting from the rear end of the female connector 10. Core wires 23, 24 at one end side of a microphone cable 20 and a connection end 25 that is an extending part of a shield outer jacket are connected to the terminals each by soldering, respectively. Around the outer peripheral side of the microphone cable 20, an insulating sleeve 60 is passed, from the rear side of which is passed a crimping sleeve 30, furthermore from the rear side of which is passed a bush 40.
The insulating sleeve 60 surrounds a connection portion between the one end side of the microphone cable 20 and the female connector 10 to protect this connection portion and prevent this connection portion from shorting, and is a member having approximately the same outer diameter as that of the female connector 10.
The crimping sleeve 30 includes a small-diameter cylindrical part 32 and a large-diameter cylindrical part 31, and between the small-diameter cylindrical part 32 and the large-diameter cylindrical part 31 there is formed a step extending radially. The crimping sleeve 30 is made of conductive material and functions as a shielding member. The large-diameter cylindrical part 31 surrounds, with a certain spatial allowance, a connection portion between the one end side of the microphone cable 20 and the female connector 10 and has approximately the same outer diameter as that of the insulating sleeve 60. The inner diameter of the small-diameter cylindrical part 32 is slightly larger than the outer diameter of the microphone cable 20. At the one end of the microphone cable 20, the shield outer jacket put on the outside of the core wires 23 and 24 is folded back outwardly, so that the shield outer jacket is put on an insulating coating of the microphone cable 20 to form a fold-back part 21 of the shield outer jacket. Around the outside of the fold-back part 21 of the shield outer jacket is passed the small-diameter cylindrical part 32 of the crimping sleeve 30, and by compressing this cylindrical part 32, the crimping sleeve 30 and the above-described shield outer jacket are electrically connected and the crimping sleeve 30 is coupled with the microphone cable 20.
The bush 40 includes a root part 41 having an inner diameter slightly larger than the outer diameter of the microphone cable 20, and a cover part 42 capable of covering the crimping sleeve 30 and having a diameter larger than the root part 41. The female connector 10 is engaged with the inner peripheral side of a cylindrical connector housing 50. The connector housing 50 has a length enough to cover the female connector 10, the insulating sleeve 60, and the large-diameter cylindrical part 31 of the crimping sleeve 30. The rear end outer circumference of the connector housing 50 is configured to fit into the front end inner circumference of the bush 40.
FIGS. 8A, 8B, and 8C show the order of assembly, and FIGS. 8C and 9 each show a cross section of the connector portion when the assembly is completed. As shown in FIG. 8A, the microphone cable 20 is connected to the female connector 10 by soldering each wire of the microphone cable 20 to each terminal of the female connector 10. After this soldering or before this soldering, the insulating sleeve 60 and crimping sleeve 30 are passed through the microphone cable 20, and as shown in FIG. 8B, the front end of the insulating sleeve 60 is butted against the rear end of the female connector 10. Moreover, around the rear end outer circumference of the insulating sleeve 60 is fitted the front end inner circumference of the large-diameter cylindrical part 31 of the crimping sleeve 30, and at the same time the small-diameter cylindrical part 32 of the crimping sleeve 30 is fitted around the fold-back part 21 of the shield outer jacket of the microphone cable 20 so as to surround this from the outside. Then, the small-diameter cylindrical part 32 of the crimping sleeve 30 is compressed from the outer peripheral side to couple the crimping sleeve 30 with the microphone cable 20 and at the same time to connect the shield outer jacket of the microphone cable 20 and the crimping sleeve 30 so as to be electrically integrated.
Then, as shown in FIGS. 8C and 9, the female connector 10, the insulating sleeve 60, and the rear end outer circumference of the connector housing 50 put on the large-diameter cylindrical part 31 of the crimping sleeve 30 are engaged with the front end inner circumference of the bush 40 to thereby integrate the connector housing 50 with the bush 40. This constitutes a connector portion at the female side, wherein the female connector 10, the insulating sleeve 60, the crimping sleeve 30, and the microphone cable 20 are integrally coupled along with the connector housing 50 and the bush 40.
According to a microphone connector of Patent Document 3 described above, the connection portion between the female connector 10 and the microphone cable 20 is covered with the large-diameter cylindrical part 31 of the crimping sleeve 30, and the small-diameter cylindrical part 32 of the crimping sleeve 30 is engaged with the outer peripheral side of the fold-back part 21 of the shield outer jacket at the end of the microphone cable 20 and is also compressed to be electrically connected with the shield outer jacket of the microphone cable 20 and moreover the large-diameter cylindrical part 31 of the crimping sleeve 30 and the connector housing 50 engage each other. Accordingly, the connection portion between the female connector 10 and the microphone cable 20 is shielded continuously from the shield outer jacket of the microphone cable 20 to the connector housing 50, thus increasing the shield effect of the connection portion between the female connector 10 and the microphone cable 20. Moreover, the connection portion between the female connector 10 and the microphone cable 20 is covered with the crimping sleeve 30 of the integral structure having the small-diameter cylindrical part 32 and the large-diameter cylindrical part 31, the small-diameter cylindrical part 32 is electrically connected to the shield outer jacket of the microphone cable 20 by compression, and the large-diameter cylindrical part 31 is electrically connected by the engagement with the connector housing 50. Accordingly, a connection from the shield outer jacket of the microphone cable 20 to the connector housing 50 is made electrically reliably and there is no open portion (opening) of the shield, thus contributing to an improvement in the shield effect of the above-described connection portion. Because the step extending radially is formed between the small-diameter cylindrical part 32 and the large-diameter cylindrical part 31 of the crimping sleeve 30, the above-described step shields effectively high frequency signals attempting to enter from the outside, thus contributing to an improvement in the shield effect of the above-described connection portion also from this point.
Because the small-diameter cylindrical part 32 of the crimping sleeve 30 is compressed at the fold-back part 21 of the shield outer jacket of the microphone cable 20, the shield outer jacket of the microphone cable 20 and the crimping sleeve 30 are connected reliably, thereby allowing the electrical contact resistance to be reduced, thus contributing to an improvement in the shield effect of the above-described connection portion also from this point.